Hard and Hybrid Coatings for Cutting and Forming Tools, and Surface Engineered Components

Thursday, May 3, 2001 8:30 AM in Room Town & Country

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8:30 AM G4-1-1 Novel Methods for Testing and Evaluating Advanced Coatings on Multi-point Cutting Edges
M. Sarwar (University of Northumbria at Newcastle, United Kingdom)
Wear and failure modes of multi-point cutting tools, broaches, bandsaws, and circular saws, can be different to single point tools owing to the mechanics of chip formation and the restriction of chip flow due to the gullet. Full product testing, and evaluating the cutting tool prior to and after surface treatment, is time consuming and expensive. Therefore there is a need for a time-compression technique for testing coatings applied to multi point cutting tools.@paragraph@ The paper describes a test method and results obtained from a single tooth test suitable for evaluating surface treated single tooth cutting edge samples. @paragraph)The result should be of immense value to both coating centres and product manufactures.
9:10 AM G4-1-3 Development, Characterization and Application of PVD-Hardcoatings for SSM-Forming of Aluminum
T. Hornig, E. Lugscheider, K. Bobzin (University of Technology (RWTH) Aachen, Germany)
The lifetime of dies for forming is mainly determined by the exposition environment. To develop coatings for enhanced lifetime a close look on the environmental characteristics is necessary. Consequently the testing procedure for lifetime increasing coatings on dies has to be divided in fundamental, simulated and finally practical testing under industrial conditions. This report follows the development of several Chromium based PVD-coatings (CrAlN, CrN, CrCN, TiN as reference) through this testing procedure. It derives the testing strategy from the semi solid metal (SSM) forming process windows, which are specified by industrial users of this process. Fundamental testing was done by mechanical (scratchtest, nanoindentation), structural (scanning electron microscope, X-ray diffraction) and chemical investigations (EDX). The simulated tests were impact-, immersion-test and thermal shock. Finally investigations under industrial conditions were performed. The investigations showed that the coatings of CrAlN and CrN had a clear superiority especially concerning their chemical stability after the immersion tests. It will be shown that for some coatings the aluminum smelt detaches from the films independently and without mechanical intervention or during metallographic preparation. Local defects led to immediate physical corrosion of the underneath material and deterioration of the PVD-coatings. Practical tests were performed under industrial conditions with and without release agents. The tests showed that a good quality of the coatings can be achieved over the whole cavity surface the aluminum components surface qualities could be drastically improved even without release agent.
9:30 AM G4-1-4 Thermal Cracking Behavior of Multi-layer LAFAD Coatings on Nitrided Die Steels in Liquid Aluminum Processing
R. Shivpuri, K. Kulkarni, A. Srivastava (The Ohio State University); R.S. Bhattacharya, S.J. Dikshit (UES, Inc.)
Thermal cracking is the primary mode of failure of large steel dies in aluminum die casting of automotive engine blocks or transmission housing. This cracking is due to large thermal shock experienced by the die steel when it is quenced by cold water after a die casting cycle. Their propagation depends on the severity of the thermal fatigue cycle (peak and range)which is caused by die surface being in contact alternatively with the liquid melt at 700@super o@C and and cold water at room temperature. Past work at The Ohio State Uniersity and Case Western Reserve University has shown that hard PVD and CVD coatings do not protect the die steel surface from cracking. On the other hand they enhance cracking. This paper presents an interesting approach at surface engineering the die to delay the onset and propagation of thermal cracks. A multilayer duplex approach is presented that provides a heat conductive ductile layer on the H-13 steel substrate which prevents thermal cracking and a multi-layer hard ceramic outer film applied by LAFAD technique that prevents reaction with the liquid melt. Reasons for the efficacy of this approach are provided as well as resulst of the laboratory and industrial evaluations. FEM modeling and simulations of the thermo-mechanical behavior of the duplex coated surface are use to understand why this coating architecture works while the single coating system fails in low cycle fatigue environment.
9:50 AM G4-1-5 Hard PVD Mutilayer Coatings Consisting of Niobium and Chromium to Protect Mild Steel Against Corrosion and Wear
P. Hovsepian, D.B. Lewis, C Schönjahn, W.-D. Münz (Sheffield Hallam University, United Kingdom); S Lyon (University of Manchester Institute of Science and Technology, United Kingdom); K Fletcher (Wilson and Co. Electroplaters, United Kingdom)
Conventionally grown columnar PVD hard coatings usually fail to protect both mild and stainless steels against corrosive attack in chloride media. The main reason for this is the formation of voids and pinholes along the grain boundaries of typically columnar grains in the coating, which produces through-holes and therefore electrochemical dissolution of the substrate material. Extensive experiments with multilayered structured PVD coatings have shown that PVD coatings may protect mild steel against corrosion in 3 % NaCl and against corrosion in salt spray, exhibiting in the potentiodynamic polarisation tests corrosion currents Ic < 5 x 10 -7 A cm -2 at a potential of 800 mV and in the salt spray tests a successful exposure time of 300 hours compared with 200 hours for electroplated 25 µm thick hard chromium layers.@paragraph@ The strict realisation of a multilayered architecture of the coating is paramount to achieve this result utilising the combined steered arc/unbalanced magnetron deposition process. The coating process is initiated by a low energetic ion implantation process employing (EI = 2.4 keV) Nb3 + ions which forms a dense amorphised 5-8 nm thick Nb film on top of the substrate surface. The coating process is continued by depositing a 1-3 µm thick metallic Nb layer. The coating process is completed by the deposition of a 4.5 µm multilayer system consisting of a 0.3 µm CrN base layer and a CrN/NbN superlattice exhibiting a period ? = 3.2 nm. Both the metallic Nb and the superlattice structured CrN/NbN layers have been deposited by unbalanced magnetron sputtering in an industrial sized multitarget PVD coating unit.@paragraph@ XRD analysis using both glancing angle and Bragg-Brentano geometry revealed a high compressive stress of –6.5 GPa and a {200} texture in the CrN/NbN multilayer being typical for direct deposition on steel substrate and for non-coherent growth of the CrN/NbN superlattice resulting from continued re-nucleation during film deposition. The coating was found to be extremely smooth (Ra = 0.033 µm) indicating a small amount growth defects. Finally XTEM analysis of the coating showed dense microstructures in all three regions consisting of a Nb, CrN and CrN/NbN superlattice coating.
10:10 AM G4-1-6 Application of PVD-Coatings on the Surface of Plastic Injection Moulds to increase productivity and product quality
W.S. Fleischer, G.J. van der Kolk, T. Hurkmans, C. Strondl, N Baranski (Hauzer Techno Coating Europe BV, The Netherlands); T. Eulenstein, U. Hinzpeter (Kunststoff Institut Lüdenscheid, Germany)
PVD coatings on surface areas of plastic injection moulds with different single- and multi layers will increase the quality of the plastic products over the complete lifetime of the mould, especially on surfaces with special structures, CrN and TiAlCN-coatings will be characterized by thermo wave analysis and the new method White Light Distance Measuring. Based on different thermal conductivities of different PVD coatings and on mould surfaces the productivity of the injection process could be increased by the right PVD coating. Results for different layer structures will be presented. A lot of industrial problems in this field can be solved by realizing anti-sticking performances on the mould surface by PVD coatings.
10:30 AM G4-1-7 Fatigue Properties of a 316L Stainless Steel Coated with Different TiN@sub x@ Deposits
J.A. Berríos (Universidad Central de Venezuela); D.G. Teer (Teer Coatings Ltd., United Kingdom); E.S. Puchi-Cabrera (Universidad Central de Venezuela)
The effect of different TiNx deposits on the fatigue properties of a 316L stainless steel has been investigated. Standard tensile and fatigue samples of the substrate material were coated industrially by close field unbalanced magnetron sputtering (PVD) at Teer Coatings Ltd. Hartlebury, U. K., with TiN0.55, TiN0.65 and TiN0.75 deposits of approximately 3µm thick. The samples were subsequently tested under rotating bending conditions in order to determine both the fatigue strength and fatigue limit of both the coated and uncoated substrate. The fatigue fracture surfaces of the coated samples were analyzed by means of scanning electron microscopy (SEM) and EDS techniques in order to determine the crack initiation sites and to study the cracks propagation throughout the transverse and longitudinal sections of the samples. It has been determined that the application of such coatings to the steel substrate gives rise to a significant increase in the yield stress of the composite material, evaluated in tension, and also of both fatigue life and fatigue limit. From the microscopic point of view it has been observed that the deposit applied remains well adhered to the substrate during tensile and fatigue testing. Also, it has been determined that the fatigue cracks originate from the surface of the coatings, rather than from the substrate-deposit interface. It has been concluded that the increase in fatigue properties of the coated substrate is related with the intrinsic higher mechanical properties of the deposits with respect to those of the substrate and to the apparent good adhesion of the deposits.